A business group has spoken out against Shane Jones' use of parliamentary privilege to attack Countdown, while the Commerce Commission has denied claims it's conducting a wide-ranging supermarket probe.

Today in Parliament, Commerce Minister Craig Foss announced that after a week of inquiries, the competition regulator was formally investigating the sector.

"I can confirm that the Commerce Commission has launched a formal investigation into the supermarket sector of New Zealand."

But the commission has since said the investigation only relates to Australian-owned Woolworths.

"The Commerce Commission has confirmed it is formally investigating the allegations of anti-competitive behaviour towards suppliers by Countdown," the regulator said in a statement.

"The investigation will involve seeking a wide range of information from a variety of sources, including organisations from all areas of the supermarket sector. The investigation is expected to take a number of months."

Meanwhile, BusinessNZ Chief executive Phil O'Reilly said repeated use of parliamentary privilege could cause significant reputational and commercial risk. Its use could cause a "chilling effect" among businesses.

"The [Countdown] matter was referred to the Commerce Commission nine days ago, but allegations have continued in Parliament over several days since this time," O'Reilly said.

For more than a week Jones has been using the protection of Parliament to accuse Countdown of "mafioso" tactics, alleging blackmail.

O'Reilly said some of the allegations made by Jones related to criminal behaviour, including alleged blackmail and fraud, and no claims have yet been made to police.

"This puts the subject of the allegations in the position of being tried in what is effectively a kangaroo court - with serious allegations made but not justified with evidence in a proper judicial process," O'Reilly said.

"This poses risk not only for the company that is the target of the current allegations, but for any other company that may be treated similarly in the future."

JONES RESPONDS

On the way to a meeting with the Commerce Commission this afternoon, Jones signalled he might cease making allegations, but felt he had been vindicated.

"It's time for me to move on from the hyperbole," Jones said, saying he had never intended that staff at Countdown would face attacks from the public, as has been claimed.

"I have to book it as a win, but the true winners, hopefully, at the end of the day, are those of us who buy our groceries for a sharper price and the suppliers who keep employing people and hopefully stay in business," Jones said.

Economic Development Minister Steven Joyce said yesterday Jones might have "over-egged" the claims.

Finance Minister Bill English suggested today that the Labour MP might have undermined the investigation.